The 27-year-old, who won Olympic gold at Vancouver 2010, travelled to Switzerland as the World Cup champion-elect with six wins from the eight rounds this season and only one left.
And Humphries, being pushed by Chelsea Valois, continued her dominance as the World Championships officially got under way in St Moritz leading after the first run and holding onto it after the second.
The Canadian, who won the world title for the first time last year with Jennifer Ciochetti in Lake Placid, clocked 1:08.18minutes on her first run, 0.12seconds better than that of Elana Meyers in second.
Just 0.15 separated Meyers in second and Esme Kamphuis of the Netherlands in sixth with three German sleds, those of Anja Schneiderheinze, Cathleen Martini and Sandra Kiriasis, in between.
The gap widened after the second run and the order changed but Humphries remained in first, and in the lead by 0.12, this time ahead of Schneiderheinze.
Humphries clocked the second fastest time second time out, 1:07.88 with Schneiderheinze jumping up from third to second after posting the quickest, 1:07.81.
Meyers was the third best in 1:07.94 to drop to third, 0.06 behind, with Martini fourth by another 0.15, Kiriasis fifth by another 0.27 and Kamphuis still sixth by another 0.14.
Meanwhile of Britain's three crews entered, Paula Walker and Gillian Cooke, who finished seventh last year, are placed 11th, improving their first run of 1:09.02 to 1:08.82 second time out.
Cooke won the world title with Nicola Minichiello in 2009 but has suffered an injury-hit season, much like Walker, while Victoria Olaoye and Kelly Denyer are ranked 19th.
They recorded two runs of 1:09.43 while the third British crew of Mica McNeill and Nikki McSweeney, like Walker, showed improvements after two runs in St Moritz.
McNeill and McSweeney, who won bronze at the Junior World Championships in December, clocked 1:10.12 and then 1:09.80 to place 20th overall.